We are using Mailhog fairly extensively at work on test instances and members of development teams have been mentioning an issue with regards to underscores in links in the HTML body being wrongly interpreted as spaces.

For example if the email body has a link email_activation it gets interpreted as email%20activation. This apparently happens for all links that use underscores as we also see this glitch with image names that contain underscores that then just 404.

I hope this makes sense and if we need to investigate further I will involve some of my developer colleagues to shine some more light on this.